Our broad, long-term objective for Phase II is to develop an immunoassay to diagnose individuals carrying a hereditary nonpolyposis colon cancer (HNPCC) trait. There are >2.5 million HNPCC-carriers in the western world; they have >80% lifetime risk for cancer; if identified, cancer prevention strategies (eg, colonoscopy to remove premalignant lesions) would greatly increase their survival. Most (>95%) carriers have a germline mutation in one of two wild type alleles for a DNA mismatch repair (MMR) gene & they should have 50% reduction in a wild type MMR protein. This prediction was supported by our study of 42 lymphoblastoid & 11 control cell lines from colorectal cancer (CRC) patients in our familial CRC Registry. Controls showed western blot bands for full-length MSH2 and MLH1 of nearly equal signal intensity. In 7 of the 42 CRC patients we saw a clear imbalance in the MSH2/MLH1 ratio (p<0.0005); DNA sequencing showed that each of the 7 had an MMR mutation. We will now test the hypothesis that our immunoassay works using 1) fresh lymphocytes (WBC) and 2) either western blots (Aims 1-2) or a sandwich-type format (Aims 3-4). Aim 1. To do a retrospective study (on 25 trait carriers & 25 controls, all pre-confirmed by DNA sequencing), to establish a positivity criterion (MSH2/MLH1 ratio) for the western blot assay using fresh WBC. Aim 2. To do a prospective study (ratio & genotype for 120 individuals at high risk (approximately 40%) for the trait) to determine test performance characteristics (sensitivity, specificity) when fresh lymphocytes & western blots are used. Aim 3. To advance the immunoassay (using cell lines with known MMR mutations) into a manual prototype of an automated, magnetic bead-based, sandwich-type format that can eventually run on the widely available commercial platform of Bayer Corp. Aim 4. To conduct retrospective & prospective studies for the sandwich- type immunoassay using lymphocytes & methods from Aims 1-2. Aim 5. To study the feasibility of incorporating analyses for less frequent MMR mutations (MSH6). We predict: a) approximately 50% decrease in a wild type MMR protein in trait carriers, b) some ratio of wild type proteins (MSH2/MLH1) will accurately distinguish, with high sensitivity & specificity, between trait carriers & non-carriers. The fully developed, automated, sandwich-type assay (Phase III) will provide a practical method for early detection of HNPCC trait carriers, before they develop cancer, which should greatly reduce morbidity and mortality from hereditary CRC. [unreadable] [unreadable] [unreadable]